Pure substances and mixtures. Methods for separating mixtures

In this article we will consider what are pure substances and mixtures, methods for separating mixtures. In everyday life, each of us uses them. Are there any pure substances in nature at all? And how to distinguish them from mixtures?

Pure substances and mixtures: methods for separating mixtures

Pure substances are those that contain particles of only a certain type. Scientists believe that in nature they practically do not exist, since all of them, albeit in insignificant fractions, contain impurities. Absolutely all substances are also soluble in water. Even if you immerse in this liquid, for example, a silver ring, the ions of this metal will pass into the solution.

A sign of pure substances are constancy of composition and physical properties. In the process of their formation, the amount of energy changes. And it can both increase and decrease. To separate a pure substance into separate components it is possible only by means of chemical reaction. For example, only discilled water has a typical boiling and freezing temperature, lack of taste and smell. A decompose its oxygen and hydrogen can only be by electrolysis.

And how do they differ from the pure substances of their aggregate? Chemistry will help us to answer this question. Methods for separation of mixtures are physical, since they do not lead to a change in the chemical composition of substances. Unlike pure substances, the mixtures have a variable composition and properties, and they can be separated by physical methods.

What is a mixture

A mixture is called the aggregate of individual substances. Its example is seawater. Unlike the disciplined, it has a bitter or salty taste, boils at a higher, and freezes at a lower temperature. Methods for the separation of mixtures of substances are physical. Thus, it is possible to extract pure salt from sea water by evaporation and subsequent crystallization.

Types of mixtures

If you add sugar to the water, after a while, its particles will dissolve and become invisible. As a result, they can not be distinguished with the naked eye. Such mixtures are called homogeneous, or homogeneous. Their examples are also air, gasoline, broth, perfume, sweet and salt water, copper and aluminum alloy. As you can see, homogeneous mixtures can be in different aggregate states, but most often there are liquids. They are also called solutions.

In heterogeneous or heterogeneous mixtures it is possible to distinguish particles of individual substances. Iron and wood sawdust, sand and table salt are their typical examples. Inhomogeneous mixtures are also called suspensions. Among them, suspensions and emulsions are distinguished. The first includes liquid and solid. So, an emulsion is a mixture of water and sand. An emulsion is a collection of two liquids with different densities.

There are heterogeneous mixtures with special names. So, foam is an example of a foam, and fog, smoke, deodorants, air fresheners, antistatics are used for aerosols.

Methods for separating mixtures

Of course, many mixtures have more valuable properties than individual individual substances that make up their composition. But even in everyday life there are situations when they need to be divided. And in industry, whole processes are based on this process. For example, oil, as a result of its processing, receives gasoline, gas oil, kerosene, fuel oil, carbide and engine oil, rocket fuel, acetylene and benzene. Agree, it is more profitable to use these products, than mindlessly burn oil.

Now let's see if there is such a thing as chemical methods of separation of mixtures. Assume that we need to get pure substances from the aqueous solution of the salt. For this, the mixture must be heated. As a result, the water turns into steam, and the salt crystallizes. But in this case, there will not be a transformation of some substances into others. This means that the basis of this process are physical phenomena.

Methods for separation of mixtures depend on the aggregate state, solubility, difference in boiling point, density and composition of its components. Let's consider each of them in more detail on specific examples.

Filtration

This separation method is suitable for mixtures containing a liquid and an insoluble solid. For example, water and river sand. This mixture must be passed through the filter. As a result, clean water will pass through it freely, and the sand will remain.

Defending

Some methods of separation of mixtures are based on the action of gravity. Thus, it is possible to decompose suspensions and emulsions into pure substances. If vegetable oil gets into the water, it must first be shaken. Then leave it for a while. As a result, water will be on the bottom of the vessel, and oil in the form of a film will cover it.

In laboratory conditions, a separatory funnel is used for settling . As a result of its work, a denser liquid merges into a vessel, and the lung remains.

Sedimentation is characterized by a low rate of the process. It takes some time to form a deposit. In industrial conditions, this method is carried out in special constructions, which are called settling tanks.

Magnet action

If the mixture is made of metal, it can be separated by a magnet. For example, separate iron and wood sawdust. But do all metals have such properties? Not at all. For this method, only mixtures containing ferromagnets are suitable. In addition to iron, they include nickel, cobalt, gadolinium, terbium, dysprosium, holmium, erbium.

Distillation

This name, translated from Latin, means "dripping with drops." Distillation represents methods for separating mixtures based on the difference in boiling points of substances. Thus, even at home, alcohol and water can be separated. The first substance begins to evaporate already at a temperature of 78 degrees Celsius. Touching the cold surface of a pair of alcohol condense, passing into a liquid state.

In industry, this way, oil products, fragrances, and pure metals are obtained.

Evaporation and crystallization

These separation methods are suitable for liquid solutions. The substances that make up their composition differ in their boiling point. Thus, it is possible to obtain crystals of salt or sugar from the water in which they are dissolved. For this, the solutions are heated and evaporated to a saturated state. In this case, the crystals precipitate. If it is necessary to obtain pure water, then the solution is brought to a boil, followed by condensation of vapors on a cooler surface.

Methods for separating gas mixtures

Gaseous mixtures are separated by laboratory and industrial methods, since this process requires the availability of special equipment. The raw material of natural origin is air, coke, generator, associated gas and natural gas, which is a combination of hydrocarbons.

The physical methods for separating mixtures that are in the gaseous state are as follows:

• Condensation is the process of gradual cooling of a mixture, during which condensation of its constituents takes place. At the same time, high-boiling substances, which are collected in separators, pass to the liquid state first of all. Thus, hydrogen is obtained from the coke oven gas, and ammonia is also separated from the unreacted portion of the mixture.
• Sorption is the absorption of certain substances by others. This process has opposite components, between which the equilibrium is established during the reaction. Different conditions are necessary for the forward and reverse process. In the first case, this is a combination of high pressure and low temperature. This process is called sorption. In the opposite case, the opposite conditions are used: low pressure at high temperature.
• Membrane separation is a method that uses the property of semipermeable partitions to selectively pass molecules of various substances.
• Reflux is the process of condensation of high-boiling parts of mixtures as a result of their cooling. In this case, the temperature of the transition to the liquid state of the individual components should differ to a great extent.

Chromatography

The name of this method can be translated as "writing in color". Imagine that ink has been added to the water. If the end of the filter paper is dropped into such a mixture, it will begin to be absorbed. In this case, the water will be absorbed faster than the ink, which is associated with a different degree of sorbability of these substances. Chromatography is not only a method of separation of mixtures, but also a method of studying such properties of substances as diffusion and solubility.

So, we got acquainted with such concepts as "pure substances" and "mixtures". The first are elements or compounds consisting only of particles of a certain type. Their examples are salt, sugar, distilled water. Mixtures are a collection of individual substances. A number of methods are used for their separation. The method of their separation depends on the physical properties of its components. The main ones are sedimentation, evaporation, crystallization, filtration, distillation, magnet action and chromatography.